This invention relates to liquid hardeners and their preparation for use in soil grouting formulations.
In constructing and repairing structures such as buildings, mines, dams, underground subway tunnels and the like, it is necessary to stabilize the soil adjacent excavation areas until the permanent structure is complete. To reinforce the soil, it is known to inject a liquid mixture of chemicals into the soil which react to form a precipitate which acts as a binder to rigidify the soil against collapse when excavated from below. The liquid mixture is dimethyl ester (DME), water and sodium silicate ("soil grouting formulation") which form the solid ester salt of sodium silicate ("silica gel"). The dimethyl ester (sometimes called dibasic ester) constituent ("liquid hardener") is derived from C.sub.4 -C.sub.6 aliphatic dibasic acids and generally is a mixture of three C.sub.4 -C.sub.6 aliphatic dimethyl esters. C.sub.4 -C.sub.6 aliphatic dimethyl esters are typically a byproduct of the manufacture of adipic acid formed by esterifying the byproduct acid stream with methanol. Although the composition of the byproduct stream (and resulting dimethyl ester composition) varies, it is generally about 15 to about 30% succinic acid, about 50 to about 73% glutaric acid and about 6 to about 25% adipic acid. Dimethyl esters are commercially available from Monsanto Company, St. Louis, Mo. as Santosol.TM. and E. I. duPont Demours & Co., Wilmington, Del., U.S.A. or can be prepared by conventional methods known to those skilled in the art.
The silica gel binder forms in the soil after a finite time interval after injection ("gel time") which is usually about 60 minutes. To the best of present knowledge before this invention, this gel time was pretty well set and could not be varied once the reactants were combined. It would be desirable to control gel time to facilitate the soil grouting process.